Electrolytic reduction of organic nitro compounds



Sept. 12, E933. M. E. CUPERY ELECTROLYTIC REDUCTION OF ORGANIC NITRQ COMPOUNDS Filed July 10, 1931 INVENTOR M02770 5 CU/Jezfy ATTORNEYS Patented Sept. 12, 1933 "UNITED STATES ELECTROLYTIC REDUCTION OF ORGANIC NITRO COIHPOUNDS Martin E. Cupery, Wilmington, Del.

Application July 10, 1931. Serial No. 549,905

7 Claims. (Cl. 204---9) This invention relates to a method of and apparatus for the reduction of organic nitro compounds by electrolysis. It is applicable to the reduction of mononitro compounds, but is more particularly adapted to the reduction of polynitro compounds such for example as dinitrobenzene, trinitrobenzene, trinitrotoluene, trinitrobenzoic acid, dinitrophenol, trinitrophenol, orthonitrophenol or paranitrophenol. Other nitro 10 compounds than those mentioned may be reduced by the procedure hereinafter described, the invention being generally applicable to the recovery of the reduction products.

The method usually employed for the reduction of organic nitro compounds includes the use of reducing reagents such as zinc, tin and iron which react with acidsto liberate hydrogen and thus to bring about the desired reduction. These metals must be separated generally from the solution 29 before the reduction product, i. e., the amine or its salt, is obtained, such separations involve many difficulties and additional expense, so that the procedure is not entirely satisfactory.

It is the object of the present invention to avoid the difiiculties heretofore encountered in the reduction of organic nitro compounds and to provide a simple and eifective procedure and apparatus whereby the desired products can be obtained with the effort and cost.

30 I have discovered that organic nitro compounds are readily reduced by electrolysis in an alcoholic solution of hydrogen chloride at fairly low temperatures, provided that atmospheric oxygen is excluded. I find that atmospheric oxygen can be excluded by conducting the electrolysis in a closed cell and by maintaining in the cell an atmosphere of hydrogen chloride, preferably by introducing hydrogen chloride gas to the cell during the reduction. It is important to maintain the below C. and preferably between 20 and 30 C., although the reduction may be conducted at temperatures even below 20 C. The low temperatures are maintained preferably by the application of a suitable cooling medium such as a water bath surrounding the electrolytic cell.

It is also desirable to introduce a suitable depolarizer to the anolyte' before the reduction commences or during the continuance thereof. Materials reacting easily with chlorine, such as phenol, sulphur dioxide, ethylene or acetylene may be used as depolarizers.

The reduction may be conducted in any suitable apparatus which comprises preferably as hereinbefore indicated a cell of any suitable conelectrolyte at relatively low temperatures, i. e.,

struction adapted to exclude atmospheric oxygen from the cathode compartment. Within the cell,

I provide a porous cup made, for example, of unglazed white porcelain which surrounds the an ode, forming a compartment therefor within the cell. The cathode is made preferably of wire gauze and surrounds the porous cup. The cell should be provided with means for stirring the catholyte, preferably operated mechanically so as to ensure uniform concentration within the cathode chamber. A thermometer or other temperature measuring means should also be provided.

The closure for the cathode compartment should have an opening through which the material to be reduced may be introduced, the opening being adapted to be sealed during the reduction. Provision should be made also for the introduction and withdrawal of hydrogen chloride gas during the reduction. It may be desirable also to provide for the introduction of the depolarizing agent to the anode compartment during the reduction.

Current is supplied from any suitable source of direct current with preferably a variable resistance to regulate the current and an ammeter to indicate the amount of current supplied. The current density may vary widely, so long as it does not cause an increase in the temperature above approximately 40 C.

As an electrolyte, I prefer to employ a water solution containing approximately 95% of ethyl alcohol saturated substantially with hydrogen More dilute alcohol solutions may chloride gas.

Methyl alcobe used under some circumstances. hol also may be employed.

The anode may be of any suitable material such as graphite or any metal which does not react with hydrogen chloride. The cathode, preferably in the form of wire gauze, may be of any suitable metal or alloysuch as copper, amalgamated copper or lead.

To the apparatus as described, I introduce a suitable amount of the organic nitro compound to be reduced and subject it to electrolysis by supplying a measured quantity of electric current,

excluding atmospheric air, preferably by continuous introduction of gaseous hydrogen chloride to the cathode compartment. The reduction proceeds rapidly. The product is the hydrochloride salt of the amine, and if insoluble in the alcoholic solution it will be precipitated and may be separated by filtration at the conclusion of the operation. If the salt is soluble, it will remain in solution and may be secured by evaporation of the solvent. I

In the accompanying drawing I have illustrated a suitable apparatus for the practice of the invention. It will be understood that the drawing is diagrammatic and that various changes may be made therein, particularly in adapting the procedure for commercial operation.

Referring to the drawing, 5 indicates the cell which may be of any suitable material such as glass or glazed earthenware. The cell is supported in a water bath 6, which may be supplied with cooling water by a pipe '7, the water escaping through an overflow pipe 8. By regulating the flow of water, the desired temperature may be readily maintained. Other suitable cooling means may be employed.

The cell 5 is closed by a cover 9 which 'closely fits the top thereof. Atmospheric oxygen may be excluded by the use of wax or other sealing means applied to the joint between the closure and the wall of the cell. A porous cup 10 of unglazed earthenware is secured to the closure 9, and an anode 11 of any of the materials hereinbefore described or other suitable materials extends into the compartment formed by the porous cup 10. The anode surface may be extended by supplemental rods 12 disposed within the porous cup and electrically connected with the anode.

A cathode 13, preferably of wire gauze made from suitable metal, surrounds the porous cup 10. The anode and cathode are connected by conductors 14 and 15 to a source of current, a variable resistance 16 and an ammeter 17 being provided in the circuit to regulate the supply of current and to indicate the amount of current supplied.

A stirrer 18 passes through the closure 9 and is adapted to be operated by a motor 19 or other driving means, a suitable stuffing box such as a mercury seal 20 being provided to prevent entrance of atmospheric air. A thermometer 21 passes through the closure. The stirrer and the thermometer are immersed in the electrolyte 22 within the cell. A pipe 23 extends through the closure 9 and into the electrolyte to permit the introduction of hydrogen chloride during the reduction.

A filling opening 24 is provided in the closure 9 and is normally closed by a plug 25 which carries a pipe 26 through which the hydrogen chloride gas may escape.

It will be understood that a suitable electrolyte as described is provided and that the temperature thereof is maintained substantially constant during the operation by the constant stirring and by regulation of the water bath surrounding the cell, current being supplied in sufficient quantity to effect the desiredelectrolysis without unduly increasing the temperature of the electrolyte.

As hereinbefore indicated, the procedure may be employed for the reduction of a variety of organic nitro compounds and is especially adapted to the treatment of polynitro compounds. As an example of the procedure, I may introduce 15 grams of 2-4 dinitrophenol to the electrolyte consisting of an alcoholic hydrogen chloride solution, and electrolyze it with a current of 4 amperes until 32 ampere hours have been used.

The solution is stirred rapidly and the temperature is maintained below 35 C. About 50 grams of phenol are used to absorb the chlorine generatedin the anode compartment. Hydrogen chloride gas is introduced continuously during the reduction, and atmospheric air is excluded. The hydrochloride salt of the amine is precipitated as the reduction proceeds. When the reduction is completed, the cathode is removed and the adhering salt dissolved in a small quantity of alcohol and water. The solution thus obtained is poured into the catholyte solution and permitted to stand a few minutes for precipitation. The solution is then. rapidly filtered, and the residue washed with several quantities of dry ether. A yield of 12.3 grams of grayishcolored 2,4-diaminophenol hydrochloride is obtained, or 76.7% of the theoretical yield.

The foregoing example merely illustrates the procedure, and similar results are obtainable by the reduction of other organic nitro compounds under the condition specified. The conditions may be varied. It is essential, however, to exclude atmospheric oxygen. The temperature must also be relatively low, preferably between 20 and 30 C. or lower, to prevent rearrangement of the hydrazo intermediates into benzidene or similar derivatives.

Various changes may be made in the details of the procedure as well as in the apparatus employed without departing from the invention or sacrificing any of the advantages thereof.

I claim:

1. The method of reducing organic nitro com pounds which comprises subjecting the compound in an alcoholic solution of hydrogen chloride to electrolysis and maintaining an atmosphere of hydrogen chloride above the catholyte.

2. The method of reducing organic nitro compounds which comprises subjecting the compound in an alcoholic solution of hydrogen chloride to electrolysis, maintaining an atmosphere of hydrogen chloride above the catholyte and introducing a depolarizer at the anode.

3. The method of reducing organic nitro compounds which comprises subjecting the compound in an alcoholic solution of hydrogen chloride to electrolysis at a temperature below 30 C. and excluding atmospheric oxygen by introducing hydrogen chloride during the reduction.

4. The method of reducing organic nitro compounds which comprises subjecting the compound in a concentrated alcoholic solution of hydrogen chloride to electrolysis at a temperature below 30 C., and excluding atmospheric oxygen by introducing hydrogen chloride during the reduction. 4

5. The method of reducing organic nitro compounds which comprises subjecting the compound in an alcoholic solution of hydrogen chloride to electrolysis at a temperature between 20 and 30 0., and excluding atmospheric oxygen by introducing hydrogen chloride during the reduction.

6. The method of 'reducing di-m'tro phenol which comprises subjecting the compound in an alcoholic solution of hydrogen chloride to electrolysis at a temperature between 20 and 30 C. and excluding atmospheric oxygen by bringing hydrogen chloride into contact with the solution during the reduction.

'7. The method of reducing di-nitro phenol which comprises subjecting the compound in an alcoholic solution of hydrogen chloride to electrolysis maintaining an atmosphere of hydrogen chloride above the catholyte and introducing a depolarizer at the anode.

MARTIN E. CUPERY. 

